•High strength concrete becomes very ductile with the addition of steel fibers.•The shear cracking is very much restrained with the use of sufficient quantity of steel fibers.•The steel fibers ...contribution to the shear strength of high strength concrete is investigated.•A proposed model is calibrated against experimental data and compared to exiting models.
Shear failure of reinforced concrete beams is generally affected by a large number of parameters among which the a/d ratio (shear-span/effective depth) is the most important. The other main parameters are the compressive strength, the longitudinal reinforcement ratio, the aggregate and the presence of transverse stirrups. The addition of steel fibers as reinforcement could be another parameter which contributes to the shear resistance. Such shear contribution will be assessed qualitatively and quantitatively for high strength concrete in the present work.
Twenty four steel fiber reinforced high strength concrete beams without stirrups and with stirrups were tested in bending under two concentrated loads; the concrete beams were designed to have a pronounced shear behavior. The possibility of replacing traditional transverse reinforcement by steel fibers was studied. In this sense, the main testing parameters were the volume fraction of steel fibers, the aspect ratio of fibers and the presence of stirrups; five volume fractions of fibers were used (0%; 0.5%; 1.0%; 2.0% and 3.0%), with two aspect ratios (lf/df of 65 and 80). The experimental results show that the shear behavior of the fiber reinforced high strength concrete beams without stirrups is similar, if not better, to that of high strength concrete beams containing stirrups reinforcement. The fiber reinforced beams had very narrow diagonal cracks and improved shear strengths, particularly for fiber fractions from 1% to 3%. Based on the present experimental work, a new empirical model is proposed for the contribution of the fibers to the shear strength of high strength concrete beams. The proposed model was assessed against other existing models and against varied experimental data taken from the literature and found relatively more satisfactory.
We focus in this paper on a potential correlation between yield stress and bleeding. We suggest that the conditions under which a fresh cement paste is able to display a yield stress result from the ...competition between Brownian motion and colloidal interactions whereas the conditions under which the suspension is stable result from the competition between colloidal interactions and gravity. These competitions highly depend on the solid volume fraction of the system and on the polymer surface coverage. The correlation between yield stress and bleeding is therefore very indirect and difficult to use in practice.
Philadelphia-negative myeloproliferative neoplasms are considered to be acquired thrombophilic states. Thromboses, both arterial and venous (not rarely in unusual sites), are often the initial events ...leading to the diagnosis. After diagnosis, the yearly incidence of thrombotic events is highly variable, and ranges from approximately 1% to 10%. The identification of patients at risk who may benefit from antithrombotic therapy remains a challenge, and it is currently based on age and history of thrombotic events. However, the predictive value of these clinical characteristics is rather limited. Few prospective studies and even fewer interventional randomized studies are available, and there are no studies designed to formally validate the use of risk stratification. The implementation of laboratory parameters such as leukocytosis and/or the JAK2 V617F mutation into a scoring system may be of interest. The mechanisms at work leading to thrombosis remain largely speculative, but are likely to be complex and multifactorial, with a prominent role of cell-cell interactions, mostly owing to qualitative changes. The long-term treatment options to prevent thrombosis are, schematically, aspirin alone as primary prevention for the low-risk patients, and cytoreduction combined with aspirin for the other patients. In very low-risk young essential thrombocythemia patients, abstention can even be considered. The optimal duration of anticoagulation after a thrombotic event is not established. All antithrombotic therapies should be balanced with the hemorrhagic risk, which can also be increased in these patients.
Abstract
Insulating building envelope is an efficient way to increase building energy efficiency and minimize greenhouse gas emissions related to heating. After building refurbishment, on-site ...measurements are suitable for verifying the actual thermal transmission properties of plane building components. For instance, the standard ISO 9869-1 describes a HFM method based on the measurement of surface heat flux with heat flow sensor (HFS). This method has been extensively investigated in the literature and successfully applied on vapor tight building walls. Nevertheless, hygroscopic building insulation materials (like biobased materials) are increasingly used, and heat transfer are coupled to moisture transfer within the wall. In this case, the HFS acts as a vapor barrier: it modifies the local moisture transfer and the associated latent heat flux. In this view, this study aims to clarify what it is measured with HFS in presence of moisture transfer. The question is first treated by numerical simulation of heat and moisture transfer within hygroscopic building wall. Then, experiments are carried out on hygroscopic building insulation where the moisture effects are exaggerated.
Coronavirus disease 2019 (COVID-19) is associated with extreme inflammatory response, disordered hemostasis and high thrombotic risk. A high incidence of thromboembolic events has been reported ...despite thromboprophylaxis, raising the question of a more effective anticoagulation. First-line hemostasis tests such as activated partial thromboplastin time, prothrombin time, fibrinogen and D-dimers are proposed for assessing thrombotic risk and monitoring hemostasis, but are vulnerable to many drawbacks affecting their reliability and clinical relevance. Specialized hemostasis-related tests (soluble fibrin complexes, tests assessing fibrinolytic capacity, viscoelastic tests, thrombin generation) may have an interest to assess the thrombotic risk associated with COVID-19. Another challenge for the hemostasis laboratory is the monitoring of heparin treatment, especially unfractionated heparin in the setting of an extreme inflammatory response. This review aimed at evaluating the role of hemostasis tests in the management of COVID-19 and discussing their main limitations.
Objectives
Dolutegravir (DTG) is a highly effective integrase inhibitor with a strong genetic resistance barrier and a potential role in simplified HIV maintenance treatment. We assessed the ...feasibility of DTG maintenance monotherapy and measured HIV reservoirs on DTG monotherapy.
Methods
An interventional, open‐label, single‐arm study including eight virologically suppressed HIV‐1‐infected patients switched to DTG 50 mg once daily for 24 weeks was performed. HIV‐1 RNA levels in plasma and cerebrospinal and seminal fluids were measured at baseline and week 24, as well as HIV‐1 DNA in peripheral cells and DTG concentrations in these compartments.
Results
HIV‐1 RNA remained undetectable in all samples of blood, cerebrospinal fluid and sperm throughout the 24 weeks, except for one cerebrospinal fluid sample with a value of 28 HIV‐1 RNA copies/mL at week 24. One patient discontinued the study because of a neurological side effect. There was no change in the mean HIV‐1 DNA level between baseline and week 24. Plasma and cerebrospinal fluid DTG concentrations reached therapeutic levels in all patients in these two compartments.
Conclusions
In this small sample of carefully selected patients, HIV‐1 reservoirs were well controlled on DTG monotherapy over a period of 24 weeks. Viral suppression was also maintained throughout follow‐up.
For concrete and other cement-based materials, cement hydration induces Le Chatelier contraction. This phenomenon creates negative pore water pressure, which increases the bulk and interfacial ...granular stresses and affects both the interfacial and bulk rheological behavior of the dense mineral suspension.
An original device was developed to assess this effect by simulating water suction in the cement-based materials undergoing hydration. An inert material with the same size range as cement was used to mimic the suction effects arising from water consumption, without the physical bonding effects due to cement hydration. Consequently, the effects of water pressure on friction and yield stress were measured on different mix-designs. The main results are an increase of the yield stress with negative water pressure and a decrease of this yield stress with the increase of air content.
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•The shear behavior of mineral suspensions under negative pressure is studied.•A device is designed to control negative pressure conditions.•Influences of device rigidity and tool geometry are studied.•Negative pressure in the material increases bulk and interfacial yield stresses.•The main material parameters are water pressure, air content and compressibility.
Fresh cement paste permeability is a key parameter to understand the hydro-mechanical behavior of cement-based materials, i.e., rhelogical properties and static stability. However, its permeability ...measurement is not easy to assess. The porous medium is not rigid and tends to change due to hydration kinetics. Two measurement methods, with 70
mm and 20
mm initial height specimens respectively, are presented and compared in this paper. The first uses a basic cell of soil permeability measurement and consists of simultaneous consolidation and percolation tests. The second uses a displacement-controlled oedometer cell equipped with pore water pressure transducers, and consists in inducing consolidation to a given void ratio first and, consecutively, in accurately measuring the permeability. A good correlation of results is observed. A comparison with theoretical models confirms that, from one fitted parameter relative to particle characteristics, a relationship between permeability and void ratio can be established.
For perfect and homogeneous plastic materials, the extrusion stress and flow typology have previously been well described. However for firm pastes, during extrusion, liquid phase migration may appear ...leading to unsuccessful processing. Reviewed literature explains that there is a competition between the extrusion velocity and the liquid filtration velocity (or time).
The aim of this work is to develop a new model to predict the ram extrusion force of frictional plastic materials such as firm fresh cement-based materials or clay pastes. A quantitative one-dimensional model based on consolidation theory has been developed to predict the extrusion force and quantify liquid phase migration.
Model results are compared with experimental data from tests carried out on kaolin paste undergoing ram extrusion. Influences of extrusion rate, rheological parameters and filtration characteristics on extrusion load are investigated.
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•Modelling the ram extrusion load of a firm paste undergoing drainage•Establishing a continuous transition from plastic to frictional plastic behaviour•Use of the consolidation theory to estimate the drainage rate•The modelling fits experimental tests performed on kaolin paste.
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